Prosecutors quoted by Fox News said they were seeking to charge Noor Salman as an accessory to 49 counts of murder and 53 counts of attempted murder, as well as with failure to warn authorities about the impending attack.

It was possible that Mateen had called his wife from inside the club while the killings were taking place, Fox quoted a source as saying.

Although Ms Salman has been questioned since the attack early on Sunday, she has not been arrested.

US Senator Angus King, a member of the Senate Intelligence Committee which received a briefing on the investigation, told CNN that “it appears she had some knowledge of what was going on”.

“She definitely is, I guess you would say, a person of interest right now and appears to be co-operating and can provide us with some important information,” he added.

Image copyrightReuters

Image caption
President Obama is due to visit the scene of the attack on Thursday

On Tuesday, US media reported that Noor Salman had gone with Omar Mateen to buy ammunition and had also driven him to the Pulse nightclub on a previous occasion because he had wanted to survey it.

However, she said she had tried to talk her husband out of carrying out the attack, sources quoted by NBC News said.

Mateen’s father, Seddique Mateen, said on Tuesday that Ms Salman – his son’s second wife – had returned to the couple’s flat on Monday to pick up some clothes. He said she and the couple’s young son were still in Florida but declined to say where.

Mateen, 29, who was killed when police stormed the club, pledged allegiance to so-called Islamic State (IS) during the attack, authorities say.